Lamellarin D Bioconjugates II: Synthesis and Cellular Internalization of

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Bioconjugate Chem. 2009, 20, 1112–1121

Lamellarin D Bioconjugates II: Synthesis and Cellular Internalization of Dendrimer and Nuclear Location Signal Derivatives Daniel Pla,†,‡ Marc Martı´,† Josep Farrera-Sinfreu,†,§ Daniel Pulido,‡,§ Andre´s Francesch,| Pilar Calvo,| ´ lvarez*,¶,†,‡ Carmen Cuevas,| Miriam Royo,‡,§ Rosa Aligue´,⊥ Fernando Albericio,*,#,†,‡ and Mercedes A Institute for Research in Biomedicine, Barcelona Science Park-University of Barcelona, Baldiri Reixac 10, E-08028 Barcelona, Spain, CIBER-BBN Networking Centre on Bioengineering, Biomaterials, and Nanomedicine, Combinatorial Chemistry Unit Barcelona Science Park (UQC-PCB), Pharma Mar S. A., Avda de los Reyes 1, E-28770 Colmenar Viejo, Madrid, Spain, and Department of Cell Biology, Faculty of Medicine, University of Barcelona, Casanova 143, E-08036 Barcelona, Spain. Received November 24, 2008; Revised Manuscript Received March 24, 2009

The design and synthesis of Lamellarin D conjugates with a nuclear localization signal peptide and a poly(ethylene glycol)-based dendrimer are described. Conjugates 1-4 were obtained in 8-84% overall yields from the corresponding protected Lamellarin D. Conjugates 1 and 4 are 1.4- to 3.3-fold more cytotoxic than the parent compound against three human tumor cell lines (MDA-MB-231 breast, A-549 lung, and HT-29 colon). Besides, conjugates 3 and 4 showed a decrease in activity potency in BJ skin fibroblasts, a normal cell culture. Cellular internalization was analyzed, and a nuclear distribution pattern was observed for 4, which contains a nuclear localization signaling sequence.

INTRODUCTION Actively mediated cellular delivery of biomolecules (1) has garnered great interest as a strategy for delivering cancer chemotherapeutics (2-5). Conjugates of a drug and a macromolecular vehicle such as NLS1 peptidic sequences (5-8), PEG carriers (9), and dendrimers (10) may have better cellular internalization than the drug alone and, in some cases, may produce passive accumulation of the drug in tumors by the EPR effect (11). In addition, the therapeutic activity of these conjugates is associated with their capacity to release the drug at a specific subcellular target. Thus, the suitability of macromolecules as vehicles also extends to their propensity to deliver the drug to a predetermined intracellular location. The marine alkaloid Lam-D (12-15) is a promising drug candidate due to its Topo I inhibition activity. Topoisomerases are nuclear enzymes crucial in cellular replication. They change the topology of DNA before and after the replication and transcription processes. Therefore, they are especially attractive targets for cancer therapy (16-19). Lam-D is limited by its insolubility in common solvent media, especially in water. Therefore, it has been used to investigate its conjugation to macromolecules. In the previous paper, we have described the first generation of Lam D-bioconjugates based on PEG esters such as 1 (9). In this paper, we describe a second generation of * Corresponding author. M.A. and F.A., Institute for Research in Biomedicine, Barcelona Science Park-University of Barcelona, Baldiri Reixac 10, E-08028 Barcelona, Spain. Tel.: +34934037086; Fax: +34934037126; E-mail [email protected]. † Barcelona Science Park-University of Barcelona. ‡ CIBER-BBN Networking Centre on Bioengineering, Biomaterials, and Nanomedicine. § Combinatorial Chemistry Unit - Barcelona Science Park (UQCPCB). | Pharma Mar S. A. ⊥ Faculty of Medicine, University of Barcelona. # Department of Organic Chemistry, University of Barcelona, E-08028 Barcelona. ¶ Laboratory of Organic Chemistry, Faculty of Pharmacy, University of Barcelona, E-08028 Barcelona.

Lam-D conjugates (Figure 1) based on esterification with either a poly(ethylene glycol)-based dendrimer (in 2) or NLS oligopeptide sequences (in 3 and 4). The peptide NLS H-Pro-ProLys-Lys-Lys-Arg-Lys-Val-OH, which has been demonstrated (20) to shuttle compounds to the nucleus, was used in the present work. The introduction of such oligomeric systems to Lam D demanded an integrated and robust synthetic scheme with a collection of suitable orthogonal protecting groups, in terms of selective removal and compatibility with the presence of other functional groups (21).

EXPERIMENTAL PROCEDURES General Data. Reagents and solvents were purified according to Purification of Laboratory Chemicals, Armarego, W. and Chai C., Elsevier (2003). Melting points (m.p.) were determined 1

Abbreviations: AU, absorbance units; A-549, lung carcinoma cell line; Bn, benzyl; Boc, tert-butoxycarbonyl; Cbz, benzyloxycarbonyl; CIQ, cellular internalization quotient; DDQ, 2,3-dichloro-5,6-dicyanop-benzoquinone; DIPCDI, N,N′-diisopropylcarbodiimide; DIPEA, diisopropylethylamine; DMAP, 4-dimethylaminopyridine; DMEM, Dulbecco’s modified Eagle’s medium; DMF, dimethylformamide; DMSO, dimethylsulfoxide; DTPA, diethylenetriamine-N,N,N′,N′,N”-pentaacetic acid; EDC · HCl, N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride; EPR, enhance permeability and retention; FACS, fluorescence-activated cell sorting; FBS, fetal bovine serum; GFP, green fluorescent protein; HOAt, 1-hydroxy-7-azabenzotriazole; HOBt, 1-hydroxybenzotriazole; HT-29, colon carcinoma cell line; GI50, 50% growth inhibition; iPr, isopropyl; Lam, Lamellarin; MDA-MB-231, breast adenocarcinoma cell line; MOM, methoxymethyl; MSNT, 1-(mesitylene-2-sulfonyl)-3-nitro-1H-1,2,4-triazole; MW, microwave; NLS, nuclear location signal; NMI, N-methylimidazole; Pbf, (2,2,4,6,7-pentamethyldihydrobenzofuran-5-sulfonyl); PBS, phosphate buffered saline; PEG, poly(ethylene glycol); PS, polystyrene; PyBOP, (benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate, SRB, sulforhodamine B; TBAF, tetrabutylammonium fluoride; TBDPS, tert-butyldiphenylsilyl; TBME, tert-butyl methyl ether; tBu, tert-butyl; TCFH, N,N,N′,N′tetramethylchloroformamidinium hexafluorophosphate; TFFH, N,N,N′,N′tetramethylfluoroformamidiniumhexafluorophosphate;TFA,trifluoroacetic acid; THF, tetrahydrofurane; Topo, Topoisomerase.

10.1021/bc800504t CCC: $40.75  2009 American Chemical Society Published on Web 05/27/2009

Lamellarin D-NLS and DTPA Conjugates

Bioconjugate Chem., Vol. 20, No. 6, 2009 1113

Figure 1. Structures of Lam-D conjugates.

in a Bu¨chi Melting Point B540 in open capillaries and are uncorrected. Automatic flash chromatography was done in an Isco Combiflash medium-pressure liquid chromatograph with Redisep silica gel columns (47-60 µm). Sonication was performed in a Branson ultrasound bath. 1H NMR and 13C NMR spectra were recorded on a Varian Mercury 400 MHz spectrometer and a Gemini 200 MHz spectrometer. Multiplicity of the carbons was assigned with DEPT and gHSQC experiments, using standard abbreviations for off-resonance decoupling: (s) singlet, (d) doublet, (t) triplet, (q) quartet. The same abbreviations were also used for the multiplicity of signals in 1H NMR, plus (m) multiplet, (bs) broad singlet, (bd) broad doublet. Spectra were referenced to appropriate residual solvent peaks (d6acetone, d6-DMSO, d4-MeOH, or CDCl3). IR spectra were obtained on a Thermo Nicolet FT-IR spectrometer. HRMS were performed on a Bruker Autoflex high-resolution mass spectrometer by Unidad de Espectrometrıá de Masas (Universidad

de Santiago de Compostela) and by SerVei d’Espectrometria de Masses (Universitat de Barcelona). Microwave-assisted reactions were carried out in a CEM Discover microwave. The automatic syringe pump was used as specified for controlled addition of some reactants. Reversed-phase analytical HPLC was performed on a Waters Alliance separation module 2695 using a Waters Xterra MS C18 column (150 × 4.6 mm, 5 µm) and a Waters 996 PDA detector at 254 nm. General Procedures. A. General Method for Simultaneous RemoVal of TBDPSO and N-Boc. HF (5 mL) at -196 °C was poured over solid 11, 12, or 14 (0.05-0.08 mmol). The solution was stirred for 1 min, and the solvent was immediately removed under vacuum at low temperature. MeCN was added to the crude, and the deprotected compound was precipitated by addition of MTBE, cooling to 0 °C and centrifugation (10 min, 2000 rpm). The residue was dried in vacuo to give the final Lam-D conjugates 1-3.

1114 Bioconjugate Chem., Vol. 20, No. 6, 2009

B. General Method for MOMO Deprotection. Me3SiI (142 µL, 3.00 mmol) was added at r.t. to a solution of 10a or 10b (1.00 mmol) in CH2Cl2 (225 mL), and the resulting orange solution was stirred at r.t. for 20 min. The solvent was removed in vacuo, and the residue was dissolved with EtOAc and then washed three times with sat NH4Cl and brine. The organic phase was dried over anhydrous MgSO4, and the solvent was removed in vacuo. Purification by column chromatography on silica gel by elution with hexane/EtOAc (80:20 to 60:40) gave the title compounds (84% quant yield). C. General Method for Esterification. Synthesis of Conjugates. DMAP (0.6 mmol) and 5 (1 mmol) in dry CH2Cl2 (45 mL) were added to a solution of NHBocPEG6-OH, or BocNLS-Gly-OH (4 mmol), and EDC · HCl (4 mmol) in dry CH2Cl2 (5 mL). The resulting solution was stirred at r.t. for 2 h. The reaction mixture was diluted with CH2Cl2 and washed with sat NaHCO3 solution and brine. The organic phase was dried over anhydrous MgSO4 and the solvent removed under vacuum, to provide the title compounds 11 and 13 (89% quant yield). 3-[3-(2-(2-(2-(2-(2-(2-Aminoethoxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)propanoyloxy]Lam-D (22) (1). Following the general procedure A and starting from 11 (24, 23, and 23 mg, 0.05 mmol), a yellow solid (35 mg, 84%) was obtained. The spectroscopic data are in accordance with previous reports (9). 3-[2-(Bis(2-(bis(2-(3-(2-(2-(3-aminopropoxy)ethoxy)ethoxy)propylamino)-2-oxoethyl)amino)ethyl)amino)acetyl]LamD (22) (2). Following the general procedure A and starting from 12 (17 and 15 mg, 0.12 mmol), 2 as a yellow solid (8 mg, 36%) was obtained. 1H NMR (D2O, 400 MHz) δ 1.54 and 1.67 (2m, J ) 6.6 Hz, 8H); 1.76 and 1.83 (2m, J ) 6.6 Hz, 8H); 2.93 (2t, J ) 7.2 Hz, 4H); 2.97 (2t, J ) 7.2 Hz, 4H); 3.02-3.10 (m, 8H); 3.16-3.29 (m, 11H, OMe); 3.33-3.43 (m, 43H, OMe); 3.52-3.56 (m, 18H); 3.70 (br, 3H, OMe); 6.43 (s, 1H); 6.57 (br, 1H); 6.71 (br, 1H); 6.81-6.88 (m, 4H); 6.99 (br, 1H); 8.35 (br, 1H). 13C NMR (D2O, 100 MHz) δ 26.6 (t); 26.7 (t); 28.5 (t); 28.6 (t); 36.4 (t); 36.5 (t); 37.7 (t); 37.8 (t); 55.2 (q); 55.5 (q); 55.7 (q); 57.6 (t); 57.7 (t); 68.3 (t); 68.4 (t); 68.5 (t); 69.4 (t); 69.5 (t); 69.6 (t); 69.7 (t); 107.7 (d); 111.5 (d); 111.7 (d); 122.2 (d); 122.4 (d); 122.8 (d); 127.6 (d); 145.6 (d); 146.7 (d); 147.4 (s); 149.5 (s); 149.9 (s); 150.3 (s); 151.1 (s); 171.0 (s); 171.1 (s). MS (MALDI-TOF) 1684 (M+1, 100), 1685 (M+2, 93) 1686 (M+3, 49). HRMS m/z calcd for C82H131N12O25 1683.9342, found 1683.9346. HPLC analysis: 6.9 min retention time (94% purity), with a gradient of 0% to 100% of eluent B over 15 min using the solvent system: H2O/0.045% TFA (A) and MeCN/0.036% TFA (B). 3-[Gly-Gly-NLS]Lam-D (22) (3). Following the general procedure A and starting from 14 (28 and 17 mg, 0.16 mmol), 3 as a white solid (10 mg, 38%) was obtained. 1H NMR (DMSO-d6, 400 MHz) δ 0.83-0.88 (m, 6H, 2CH3); 1.22-1.36 (m, 10H, 5CH2); 1.42-1.54 (m, 8H, 4CH2); 1.56-1.62 (m, 8H, 4CH2); 1.88-1.93 (m, 4H, 2CH2); 2.05 (br, 2H, CH2); 2.07 (br, 2H, CH2); 2.33 (t, J ) 1.8 Hz, 2H, CH2); 2.55 (br, 1H, CH); 2.67 (t, J ) 1.8 Hz, 2H, CH2); 2.69-2.75 (m, 16H, 3CH2); 3.36 (2s, 6H, 2OMe); 3.75 (s, 3H, OMe); 3.99-4.05 (m, 3H, CH); 4.14-4.25 (m, 7H, 3CH, 2CH2); 4.58 (br, 1H, CH); 5.93 (br, 1H); 5.76 (br, 1H); 5.47 (br, 1H); 6.70 (s, 1H); 6.87 (s, 1H); 7.01 (dd, J ) 8.0, 1.7 Hz, 1H); 7.10 (d, J ) 8.0 Hz, 1H); 7.12-7.13 (m, 2H); 7.19 (s, 1H); 7.21 (br, 1H); 9.00 (d, J ) 7.4 Hz, 1H, H8). MS (MALDI-TOF) 1575 (M+1, 100), 1576 (M+2, 92). HRMS m/z calcd. for C77H111N18O18 1575.8324, found 1575.8319. HPLC analysis: 1.8 min retention time (96.7% purity), with 15 min isocratic MeCN/0.036% TFA. 4′-[Gly-NLS]Lam-D (22) (4). Peptide 8 (392 mg, 0.23 mmol) was preactivated for 15 min at r.t. with TCFH (63 mg, 23 mmol) and NEt3 (32 µL, 23 mmol) in dry CH2Cl2 (15 mL). Compound 6 (53 mg, 0.08 mmol) and DMAP (9 mg, 0.08 mmol) in dry

Pla et al.

CH2Cl2 (5 mL) were then added. The resulting solution was stirred at r.t. for 120 h. The reaction mixture was diluted with CH2Cl2 and washed with sat NaHCO3 solution and brine. The organic phase was dried over anhydrous MgSO4, and the solvent was removed under vacuum. The residue was purified by flash chromatography: elution with CH2Cl2/MeOH (99:1 to 95:5) gave 15 (45% yield based on 40% transformation of 6). The Boc protected compound 15 was then treated with 40% TFA in CH2Cl2 (10 mL) at r.t. for 1 h. The solvent was removed under reduced pressure, and the residue was purified by reverse-phase chromatography. Elution with H2O/MeCN (60:40 to 40:60) gave 4 as a yellow solid (3 mg, 17%). 1H NMR (D2O, 500 MHz) δ 1.04 (d, J ) 6.5 Hz, 3H, CH3); 1.16 (d, J ) 6.5 Hz, 3H, CH3); 1.39-1.56 (m, 8H, 4CH2); 1.66-1.77 (m, 10H, 5CH2); 1.78-1.88 (m, 8H, 4CH2); 2.00-2.12 (m, 4H, 2CH2); 2.17 and 2.36 (2br, 2H, CH2); 2.44 and 2.58 (2br, 2H, CH2); 2.84 (br, 1H, CH); 2.96-3.05 (m, 10H, 5CH2); 3.40 (br, 3H, OMe); 3.44 (s, 3H, OMe); 3.45 (s, 3H, OMe); 3.22 (t, J ) 7.5 Hz, 1H, CH2); 3.59 (t, J ) 7.0 Hz, 1H, CH2); 3.81 (br, 2H, CH2); 4.23-4.42 (m, 5H, 5CH); 4.51 (t, J ) 8.3 Hz, 1H, CH); 4.65 (dd, J ) 9.0, 8.4 Hz, 1H, CH); 6.38 (s, 1H); 6.64-6.87 (m, 4H); 6.99 (br, 1H); 7.01 (br, 1H); 7.32 (br, 1H); 8.54 (br, 1H). MS (MALDI-TOF) 1518 (M+1, 100), 1519 (M+2, 82). HRMS m/z calcd. for C75H108N17O17 1518.8109, found 1518.8114. HPLC analysis: 6.9 min retention time (95% purity), with a gradient of 50% to 100% of eluent B over 15 min using the solvent system: H2O/0.045% TFA (A) and MeCN/0.036% TFA (B). 4′,11-Bis(tert-butyldiphenylsilyl)Lam-D (22) (5). Following the general procedure B and starting from 10b (1.06 g, 1.04 mmol), 5 as a yellow solid (856 mg, 84%) was obtained. mp (MeCN) 278-280 °C. IR (film) ν 1704, 1487, 1428, 1284, 1111 cm-1. 1H NMR (CDCl3, 200 MHz) δ 1.15 (s, 9H); 1.17 (s, 9H); 3.18 (s, 3H, OMe); 3.47 (s, 3H, OMe); 3.64 (s, 3H, OMe); 5.89 (s, 1H); 6.68 (d, J ) 7.4 Hz, 1H, H9); 6.69 (s, 1H); 6.91-6.93 (m, 3H); 6.95 (s, 1H); 7.05 (br, 1H); 7.06 (br, 1H); 7.37-7.48 (m, 10H); 7.71-7.79 (m, 10H); 9.04 (d, J ) 7.4 Hz, 1H, H8). 13 C NMR (CDCl3, 100 MHz) δ 19.9 (s); 26.6 (q); 26.7 (q); 54.5 (q); 55.5 (q); 55.7 (q); 103.4 (d); 104.7 (d); 105.9 (d); 107.6 (s); 109.8 (s); 111.0 (s); 112.1 (d); 115.4 (d); 116.5 (d); 119.7 (s); 120.3 (d); 122.7 (d); 123.7 (d); 124.4 (s); 127.5 (d); 127.6 (d); 128.5 (s); 129.1 (s); 129.7 (d); 129.9 (d); 132.9 (s); 133.0 (s); 133.4 (s); 134.1 (s); 135.0 (d); 135.1 (d); 143.1 (s); 144.9 (s); 146.1 (s); 146.8 (s); 150.7 (s); 151.1 (s); 155.3 (s). MS (MALDI-TOF) 976 (M+1, 100), 977 (M+1, 57), 978 (M+2, 38). 3,11-Di-tert-butoxycarbonyl-Lam-D (22) (6). A solution of TBAF in THF (1 M, 1.64 mmol) was added to a -78 °C solution of 10d (771 mg, 0.82 mmol), in MeOH-THF (100 mL, 80:20). The mixture was stirred at -78 °C for 15 min. Solvents were removed under vacuum, and the residue was dissolved in CH2Cl2. The organic solution was washed with water and brine. The organic phase was dried over anhydrous MgSO4 and the solvent removed under vacuum. The residue was purified by flash chromatography: elution with hexane/EtOAc (60:40 to 40: 60) gave 6 as a white solid (491 mg, 85%). mp (MeCN) 149-150 °C. IR (film) ν 1760, 1709, 1275, 1255 cm-1. 1H NMR (CDCl3, 400 MHz) δ 1.54 (s, 9H); 1.55 (s, 9H); 3.455 (s, 3H, OMe); 3.463 (s, 3H, OMe); 3.91 (s, 3H, OMe); 5.93 (br, 1H, OH); 6.83 (s, 1H); 6.97 (d, J ) 7.4 Hz, 1H, H9); 7.11 (br, 1H); 7.15 (dd, J ) 8.0, 1.8 Hz, 1H); 7.18 (br, 1H); 7.24-7.26 (m, 2H); 7.44 (br, 1H); 9.14 (d, J ) 7.4 Hz, 1H, H8). 13C NMR (CDCl3, 100 MHz) δ 27.5 (q); 55.3 (q); 55.6 (q); 56.3 (q); 83.89 (s); 83.95 (s); 106.4 (d); 106.6 (d); 108.8 (s); 111.8 (d); 112.6 (d); 113.0 (s); 113.5 (d); 115.4 (d); 115.7 (s); 120.3 (d); 123.0 (d); 123.6 (s); 123.8 (s); 124.0 (s); 124.4 (d); 128.1 (s); 128.3 (s); 133.6 (s); 140.0 (s); 141.0 (s); 145.4 (s); 145.9 (s); 147.7


(s); 147.9 (s); 150.9 (s); 151.0 (s); 151.1 (s); 155.0 (s). MS (MALDI-TOF) 699 (M, 56), 700 (M+1, 100). Boc-Pro-Pro-Lys(Boc)-Lys(Boc)-Lys(Boc)-Arg(Boc2)-Lys(Boc)-Val-Gly-OH (8). The Boc protected peptide was synthesized manually on solid phase in a polypropylene syringe fitted with a porous polyethylene disk. Solvents and soluble reagents were removed by suction. Washings between deprotection, coupling, and subsequent deprotection steps were carried out with DMF (5 × 1 min) and CH2Cl2 (5 × 1 min) using 10 mL solvent/g resin each time. Standard Fmoc/tBu chemistry and chlorotrityl resin (0.5 g, 1.5 mmol/g) were used. The resin was preswollen in anhydrous CH2Cl2 and then in DMF. The first Fmoc-protected amino acid (Fmoc-L-Gly-OH) (155 mg, 0.7 equiv) was introduced in the presence of DIEA (635 µL, 5 equiv) in DMF. After 1 h, MeOH (0.5 mL) was added and the mixture was stirred for 30 min. The resin was then washed with DMF and CH2Cl2, and the synthesis continued as described below. The peptide was elongated through successive iterations of Fmoc removal and amino acid coupling. The Fmoc protecting group was removed with several treatments of 20% piperidine in DMF (1 × 1 min + 2 × 15 min). The resin was then washed with DMF and CH2Cl2. The corresponding Fmoc-protected amino acid (5 equiv) was introduced using DIPCDI (310 µL, 5 equiv) and HOBt (305 mg, 5 equiv) as coupling agents. After 2 h, the resin was washed with DMF and CH2Cl2, and the coupling was monitored using the Kaiser test. Recouplings were done when needed. Boc-L-Pro-OH (430 mg, 5 equiv) was used as a last amino acid. The peptide was finally cleaved from the resin using 3% TFA in CH2Cl2, (5 × 1 min). Washes were collected in a flask containing 50 mL of water. The CH2Cl2 was then evaporated under reduced pressure, MeCN (30 mL) was added to the aqueous solution, and the resulting mixture was then lyophilized. Peptide 8 (590 mg, 94%) was obtained as a white solid. HPLC analysis: 6.2 min retention time (92% purity), with a gradient of 50% to 100% of eluent B in 7 min using the solvent system: H2O/0.045% TFA (A) and MeCN/ 0.036% TFA (B). HPLC ESI-MS calcd. for C82H144N16O24 [M+H]+ 1738, found: [M+2]2+/2, 870. 11-Benzyl-4′-tert-butyldiphenylsilyl-3-methoxymethylLam-D (22) (10). A mixture of 9 (27) (1.54 g, 1.76 mmol) and DDQ (400 mg, 1.76 mmol) in dry CHCl3 (25 mL) was purged with Ar in a sealed vessel and microwaved at 120 °C for 10 min. The organic solution was washed with water, and brine, dried over MgSO4, filtered, and then concentrated in vacuo. Purification by column chromatography on silica gel by elution with hexane/EtOAc (80:20 to 60:40) gave 10 as a white solid (2.27 g, 81%). mp (MeCN) 144-145 °C. IR (film) ν 1705, 1429, 1267, 1223 cm-1. 1H NMR (CDCl3, 200 MHz) δ 1.17 (s, 9H); 3.43 (s, 3H, OMe); 3.46 (s, 3H, OMe); 3.50 (s, 3H, OMe); 3.65 (s, 3H, OMe); 5.23 (s, 2H); 5.24 (s, 2H); 6.77 (s, 1H); 6.92-6.96 (m, 3H); 7.06-7.08 (m, 2H); 7.19 (s, 1H); 7.25 (d, J ) 5.4 Hz, 1H); 7.32-7.47 (m, 11H); 7.75-7.79 (m, 4H); 9.16 (d, J ) 7.2 Hz, 1H, H8). 13C NMR (CDCl3, 50.3 MHz) δ 19.9 (s); 26.7 (q); 55.2 (q); 55.5 (q); 55.7 (q); 56.3 (q); 70.7 (t); 95.4 (t); 105.1 (d); 105.5 (d); 105.6 (d); 109.4 (d); 111.3 (s); 111.4 (s); 112.3 (d); 115.4 (d); 119.3 (s); 120.3 (d); 123.1 (d); 123.7 (d); 124.5 (s); 127.2 (d); 127.7 (d); 128.0 (d); 128.4 (s); 128.5 (s); 128.6 (d); 128.9 (s); 129.9 (d); 133.3 (s); 134.1 (s); 135.1 (d); 136.2 (s); 145.0 (s); 146.0 (s); 146.2 (s); 146.6 (s); 149.0 (s); 149.5 (s); 151.2 (s); 155.3 (s). MS (MALDI-TOF) 871 (M, 18), 872 (M+1, 100). 4′-tert-Butyldiphenylsilyl-3-methoxymethyl-Lam-D (22) (10a). Pd/C (10%) was added to a solution of 10 (509 mg, 0.58 mmol) in MeOH/EtOAc (2:1, 58 mL), the mixture was purged with H2, and the resulting suspension was stirred at r.t. for 16 h. The reaction mixture was filtered through a pad of Celite, which was then washed with CH2Cl2. The solvent was removed under


vacuum to provide the 10a as a brown solid (433 mg, 95%). mp (MeCN) 129-130 °C. IR (film) ν 3213, 1680, 1425, 1222 cm-1. 1H NMR (CDCl3, 400 MHz) δ 1.16 (s, 9H); 3.44 (s, 3H, OMe); 3.47 (s, 3H, OMe); 3.51 (s, 3H, OMe); 3.65 (s, 3H, OMe); 5.24 (s, 2H); 5.92 (br, 1H, OH); 6.77 (s, 1H); 6.93-6.94 (m, 2H); 6.98 (d, J ) 7.4 Hz, 1H, H9); 7.05 (br, 1H); 7.13 (s, 1H); 7.16 (s, 1H); 7.25 (d, J ) 5.6 Hz, 2H); 7.38-7.47 (m, 5H); 7.75-7.78 (m, 4H); 9.18 (d, J ) 7.4 Hz, 1H, H8). 13C NMR (CDCl3, 100 MHz) δ 19.8 (s); 26.7 (q); 55.3 (q); 55.5 (q); 55.7 (q); 56.3 (q); 95.5 (t); 105.0 (d); 105.3 (d); 105.6 (d); 110.8 (d); 111.2 (s); 111.5 (s); 112.4 (d); 115.4 (d); 118.8 (s); 120.4 (d); 123.3 (d); 123.7 (d); 125.3 (s); 127.7 (d); 128.6 (s); 129.0 (s); 129.96 (d); 129.98 (d); 133.37 (s); 133.43 (s); 134.4 (s); 135.2 (d); 135.3 (s); 145.1 (s); 146.1 (s); 146.3 (s); 146.66 (s); 146.69 (s); 146.8 (s); 151.3 (s); 155.4 (s). MS (MALDITOF) 781 (M, 60), 782 (M+1, 100). 4′,11-Bis(tert-butyldiphenylsilyl)-3-methoxymethylLam-D (10b). TBDPSCl (389 µL, 1.07 g/mL, 1.47 mmol) was added to a solution of 10a (768 mg, 0.98 mmol), imidazole (135 mg, 1.96 mmol), and DMAP (120 mg, 0.98 mmol) in dry DMF (30 mL). The mixture was stirred for 24 h under Ar. DMF was removed under reduced pressure, and the residue was dissolved in CH2Cl2. The organic phase was washed with water and brine, and then dried over anhydrous MgSO4. The solvent was removed under vacuum, and the residue was purified by flash chromatography. Elution with hexane/CH2Cl2 (40:60 to 20:80) gave 10b (584 mg, 58%) as a brown oil. IR (film) ν 1679, 1426, 1113 cm-1. 1H NMR (CDCl3, 200 MHz) δ 1.13 (s, 9H); 1.15 (s, 9H); 3.17 (s, 3H, OMe); 3.42 (s, 3H, OMe); 3.49 (s, 3H, OMe); 3.61 (s, 3H, OMe); 5.21 (s, 2H); 6.71 (d, 1H, J ) 7.4 Hz, H9); 6.74 (s, 1H); 6.90 (2s, 2H); 6.92 (s, 1H); 7.01-7.05 (m, 2H); 7.22 (br, 1H); 7.10-7.19 (m, 10H); 7.69-7.77 (m, 10H); 9.06 (d, J ) 7.4 Hz, 1H, H8). 13C NMR (CDCl3, 100 MHz) δ 19.9 (s); 26.6 (q); 26.7 (q); 54.5 (q); 55.4 (q); 55.7 (q); 56.3 (q); 95.4 (t); 105.1 (d); 105.5 (d); 105.9 (d); 107.9 (s); 111.3 (s); 111.4 (s); 112.3 (d); 115.3 (d); 116.5 (d); 119.7 (s); 120.3 (d); 122.7 (d); 123.6 (d); 124.4 (s); 127.4 (d); 127.6 (d); 127.7 (d); 127.8 (d); 128.4 (s); 128.8 (s); 129.5 (d); 129.7 (d); 130.0 (d); 132.9 (s); 133.0 (s); 133.4 (s); 134.7 (d); 135.0 (d); 135.1 (d); 144.9 (s); 145.9 (s); 146.2 (s); 146.5 (s); 150.7 (s); 151.1 (s); 155.3 (s). MS (ESI) 1020 (M+1, 100). 4′-tert-Butyldiphenylsilyl-Lam-D (22) (10c). Following the general procedure B and starting from 10a (639 mg, 0.81 mmol), 10c as a white solid (603 mg, quant) was obtained. mp (MeCN) 275-276 °C. IR (film) ν 3415, 1679, 1429, 1271 cm-1. 1H NMR (CDCl3, 400 MHz) δ 1.17 (s, 9H); 3.46 (s, 3H, OMe); 3.47 (s, 3H, OMe); 3.65 (s, 3H, OMe); 6.71 (s, 1H); 6.93-6.94 (m, 2H); 6.98-7.05 (m, 3H); 7.13 (s, 1H); 7.17 (s, 1H); 7.39-7.47 (m, 6H); 7.76-7.79 (m, 4H); 9.17 (d, J ) 7.4 Hz, 1H, H8). 13C NMR (CDCl3, 100 MHz) δ 19.9 (s); 26.7 (q); 55.3 (q); 55.5 (q); 55.7 (q); 103.6 (d); 104.7 (s); 104.8 (d); 105.0 (d); 107.8 (s); 109.9 (s); 110.8 (d); 110.9 (s); 112.3 (d); 115.5 (d); 118.8 (s); 120.4 (d); 123.4 (d); 123.8 (d); 125.4 (s); 127.7 (s); 127.9 (d); 129.3 (s); 130.0 (d); 133.4 (s); 133.5 (s); 135.2 (d); 143.2 (s); 145.1 (s); 146.2 (s); 146.7 (s); 146.8 (s); 147.0 (s); 151.3 (s); 155.5 (s). MS (ESI-TOF) 737 (M, 73), 738 (M+1, 100). 4′-tert-Butyldiphenylsilyl-3,11-bis(tert-butoxycarbonyl)Lam-D (22) (10d). (Boc)2O (536 mg, 2.45 mmol) and DMAP (30 mg, 0.25 mmol) were added to a solution of 10c (605 mg, 0.82 mmol) in CH2Cl2 (130 mL). The reaction mixture was stirred at r.t. under Ar for 16 h. The mixture was washed with sat NaHCO3 and brine. The organic layer was dried over anhydrous Na2SO4, filtered, and concentrated to dryness to give 10d as a yellow solid (767 mg, quant). mp (MeCN) 188-189 °C. IR (film) ν 1760, 1710, 1486, 1430, 1274, 1255 cm-1. 1H NMR (CDCl3, 400 MHz) δ 1.15 (s, 9H); 1.56 (s, 9H); 1.57 (s, 9H); 3.40 (s, 3H, OMe); 3.42 (s, 3H, OMe); 3.64 (s, 3H, OMe);


6.83 (s, 1H); 6.90-6.93 (m, 2H); 7.01 (br, 1H); 7.04 (d, J ) 7.4 Hz, 1H, H9); 7.23 (s, 1H); 7.25 (d, J ) 5.8 Hz, 2H); 7.38-7.46 (m, 6H); 7.74-7.77 (m, 4H); 9.22 (d, J ) 7.4 Hz, 1H, H8). 13C NMR (CDCl3, 100 MHz) δ 19.9 (s); 26.7 (q); 27.6 (q); 55.3 (q); 55.6 (q); 55.7 (q); 83.96 (s); 84.02 (s); 106.5 (d); 106.7 (d); 108.9 (s); 111.9 (d); 112.7 (d); 113.1 (s); 115.0 (d); 115.8 (s); 120.3 (d); 120.5 (d); 123.3 (d); 123.4 (d); 123.7 (s); 123.9 (s); 127.7 (s); 127.9 (d); 128.3 (s); 130.0 (d); 133.4 (s); 133.6 (s); 135.1 (d); 140.0 (s); 141.0 (s); 145.3 (s); 145.5 (s); 147.7 (s); 150.8 (s); 151.0 (s); 151.2 (s); 151.5 (s); 155.1 (s). MS (MALDI-TOF) 938 (M+1, 100), 939 (M+2, 63). 4′,11-Bis(tert-butyldiphenylsilyl)-3-[3-(2-(2-(2-(2-(2-(2-tertbutoxycarbonylaminoethoxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)propanoyl]Lam-D (22) (11). Following the general procedure C and starting from 5 (78 mg, 0.80 mmol), 11 as a yellow oil (112 mg, quant) was obtained. IR (film) ν 1710, 1486, 1429, 1283, 1159, 1114 cm-1. 1H NMR (CDCl3, 200 MHz) δ 1.04 (s, 9H); 1.06 (s, 9H); 1.36 (s, 9H); 2.81 (t, J ) 6.5 Hz, 2H); 3.07 (s, 3H, OMe); 3.24 (br, 4H, 2CH2); 3.29 (s, 3H, OMe); 3.43-3.48 (m, 4H, 2CH2); 3.52-3.60 (m, 19H, 8CH2, OMe); 3.79 (t, J ) 6.5 Hz, 2H); 5.05 (br, 1H); 6.68 (d, J ) 7.4 Hz, 1H, H9); 6.75 (s, 1H); 6.81 (br, 2H); 6.85 (s, 1H); 6.91 (br, 1H); 6.95 (br, 1H); 7.03 (s, 1H); 7.24-7.38 (m, 10H); 7.61-7.68 (m, 10H); 9.00 (d, J ) 7.4 Hz, 1H, H8). 13C NMR (CDCl3, 100 MHz) δ 19.8 (s); 26.5 (q); 26.7 (q); 28.4 (q); 34.7 (t); 40.3 (t); 54.4 (q); 55.4 (q); 55.6 (q); 66.3 (t); 70.1 (t); 70.5 (t); 105.8 (d); 106.3 (d); 108.1 (s); 111.8 (s); 111.9 (d); 112.6 (d); 115.1 (d); 116.0 (s); 116.5 (d); 119.6 (s); 120.3 (d); 122.5 (d); 123.5 (d); 124.3 (s); 127.4 (s); 127.5 (d); 127.6 (d); 128.0 (s); 128.1 (s); 129.7 (d); 129.8 (d); 132.8 (s); 132.9 (s); 133.3 (s); 134.2 (s); 134.9 (d); 135.1 (d); 139.2 (s); 144.9 (s); 145.3 (s); 146.2 (s); 147.2 (s); 150.8 (s); 151.1 (s); 154.9 (s); 169.2 (s). MS (MALDI-TOF) 1311 (M+1Boc, 100), 1433 (M+Na, 45). 4′,11-Bis(tert-butyldiphenylsilyl)-3-[2-(bis(2-(bis(2-(3-(2-(2(3-tert-butoxycarbonylamino-propoxy)ethoxy)ethoxy)propylamino)-2-oxoethyl)amino)ethyl)amino)acetyl]-Lam-D (22) (12). A mixture of polystyrene solid supported DMAP (6.0 mg, 19 mmol) and 5 (31 mg, 32 mmol) in dry CH2Cl2 (2 mL) was added to a solution of 7 (51 mg, 32 mmol) and EDC · HCl (6 mg, 32 mmol) in dry CH2Cl2 (2 mL). The resulting solution was stirred at r.t. for 16 h. The reaction mixture was filtered, and the solvent was removed under vacuum. The residue was purified by flash chromatography with neutral alumina. Elution with CH2Cl2/MeOH (99:1 to 98:2) gave 12 as a yellow oil (22 mg, 26%). IR (film) ν 3323, 1665, 1548, 1428, 1275, 1112 cm-1. 1 H NMR (CDCl3, 200 MHz) δ 1.11 (s, 9H); 1.13 (s, 9H); 1.41 (s, 18H); 1.42 (s, 18H); 1.61-1.77 (m, 16H); 2.34 (2t, 4H); 2.71-2.78 (m, 4H); 3.12 (s, 3H, OMe); 3.15-3.31 (m, 26H); 3.35 (s, 3H, OMe); 3.47-3.67 (m, 43H); 5.06 (br, 2H); 5.16 (br, 1H); 5.30 (br, 1H); 6.77 (d, J ) 7.4 Hz, 1H, H9); 6.84 (s, 1H); 6.88 (br, 2H); 6.92 (s, 1H); 6.97 (br, 1H); 7.00 (br, 1H); 7.12 (s, 1H); 7.32-7.45 (m, 10H); 7.64-7.73 (m, 10H); 9.08 (d, J ) 7.4 Hz, 1H, H8). 13C NMR (CDCl3, 100 MHz) δ 15.4 (q); 19.8 (s); 26.6 (q); 26.7 (q); 27.3 (t); 28.4 (q); 29.4 (t); 29.7 (t); 35.3 (t); 37.0 (t); 38.4 (t); 39.5 (t); 54.5 (q); 55.4 (q); 55.7 (q); 57.2 (t); 59.0 (t); 69.3 (t); 69.4 (t); 70.1 (t); 70.4 (t); 70.5 (t); 105.9 (d); 106.4 (d); 108.2 (s); 112.0 (d); 112.9 (d); 115.2 (d); 116.2 (s); 116.6 (d); 119.7 (s); 120.4 (d); 123.5 (d); 124.4 (s); 127.6 (d); 127.7 (d); 128.0 (s); 128.1(s); 129.8 (d); 129.9 (d); 130.0 (s); 132.9 (s); 133.0 (s); 133.4 (s); 134.4 (s); 135.1 (d); 135.2 (d); 138.9 (s); 145.2 (s); 145.4 (s); 146.4 (s); 147.2 (s); 150.9 (s); 151.3 (s); 154.9 (s); 156.1 (s); 159.1 (s); 169.2 (s); 170.7 (s). MS (ESI-TOF) 820 ([M-Boc+3]/3, 100). 4′,11-Bis(tert-butyldiphenylsilyl-3-(tert-butoxycarbonylaminoacetyl)-Lam-D (22) (13). Following the general procedure C and starting from 5 (99 mg, 1.02 mmol), 13 was obtained as a yellow solid (103 mg, 89%). mp (MeCN)

Pla et al.

197-199 °C. IR (film) ν 1711, 1509, 1486, 1429, 1283, 1158 cm-1. 1H NMR (CDCl3, 200 MHz) δ 1.14 (s, 9H); 1.15 (s, 9H); 1.49 (s, 9H); 3.17 (s, 3H, OMe); 3.37 (s, 3H, OMe); 3.62 (s, 3H, OMe); 4.23 (brd, J ) 5.0 Hz, 2H); 5.13 (brt, J ) 5.0 Hz, 1H); 6.73 (d, J ) 7.4 Hz, 1H, H9); 6.85 (s, 1H); 6.91 (br, 2H); 6.93 (s, 1H); 7.02 (br, 1H); 7.05 (br, 1H); 7.12 (br, 1H); 7.36-7.48 (m, 10H); 7.70-7.77 (m, 10H); 9.05 (d, J ) 7.4 Hz, 1H, H8). 13C NMR (CDCl3, 100 MHz) δ 19.9 (s); 26.6 (q); 26.7 (q); 28.3 (q); 42.3 (t); 54.5 (q); 55.5 (q); 55.6 (q); 105.8 (d); 106.4 (d); 108.1 (s); 111.7 (d); 111.9 (s); 112.7 (d); 115.2 (d); 116.3 (s); 116.6 (d); 119.7 (s); 120.3 (d); 122.5 (d); 123.5 (d); 124.3 (s); 127.5 (s); 127.6 (d); 127.7 (d); 127.9 (s); 128.1 (s); 129.6 (s); 129.7 (d); 129.9 (d); 132.9 (s); 133.3 (s); 134.2 (s); 135.0 (d); 135.2 (d); 135.4 (s); 138.8 (s); 145.0 (s); 145.3 (s); 146.3 (s); 147.0 (s); 150.8 (s); 151.2 (s); 154.8 (s); 168.3 (s). MS (MALDI-TOF) 1132 (M, 100), 1133 (M+1, 79), 1134 (M+2, 37). 4′,11-Bis(tert-butyldiphenylsilyl)-3-[Gly-Gly-Boc-NLS]Lam-D (22) (14). Lamellarin 13 (32 mg, 29 mmol) was treated with 40% TFA in CH2Cl2 (10 mL) at 0 °C for 10 min. The solvent was removed under reduced pressure, and the crude was used without further purification. A solution of this residue and DIPEA (4.9 µL, 29 mmol) in dry CH2Cl2 (3 mL) was added to a solution of 8 (50 mg, 29 mmol), HOBt (5 mg, 34 mmol), DIPEA (4.9 µL, 29 mmol), and EDC · HCl (7 mg, 34 mmol) in dry CH2Cl2 (2 mL). The resulting solution was stirred at r.t. for 4 h. The reaction mixture was diluted with CH2Cl2 and washed with sat NaHCO3 solution and brine. The organic phase was dried over anhydrous MgSO4, and the solvent was removed under vacuum. The residue was purified by flash chromatography with neutral alumina: elution with CH2Cl2/MeOH (98:2 to 95:5) gave 14 as a yellow oil (46 mg, 58%). IR (film) 3328, 1650, 1534, 1429, 1365, 1281, 1166 cm-1. 1H NMR (CDCl3, 200 MHz) δ 0.92-1.00 (m, 6H, 2CH3); 1.11 (s, 3H, CH3); 1.13 (s, 3H, CH3); 1.23-1.33 (m, 8H, 4CH2); 1.36-1.37 (m, 4H, 2CH2); 1.39 (s, 3H, CH3); 1.41 (s, 18H, 6CH3); 1.44-1.50 (m, 4H, 2CH2); 1.46-1.50 (m, 8H, 4CH2); 1.84 (br, 4H, 2CH2); 2.07 (br, 4H, 2CH2); 2.43 (br, 4H, 2CH2); 2.71 (h, J ) 6.8 Hz, 1H); 3.00 and 3.07 (2br, 8H, 4CH2); 3.14 (s, 3H, OMe); 3.34-3.41 (m, 2H, CH2); 3.44 (s, 3H, OMe); 3.59 (s, 3H, OMe); 3.62-3.74 (m, 2H, CH2); 3.92-4.23 (m, 5H, 5CH); 4.28 (br, 2H, CH2); 4.47-4.53 (m, 2H, CH2); 4.67-4.71 (m, 3H, 3CH); 4.77 (br, 1H); 4.86 (br, 1H); 6.67 (s, 1H); 6.71 (d, J ) 7.4 Hz, 1H, H9); 6.80-6.89 (m, 2H); 6.91 (d, J ) 1.8 Hz, 1H); 6.95-6.99 (m, 2H); 7.02 (d, J ) 8.2 Hz, 1H); 7.32-7.47 (m, 10H); 7.56-7.75 (m, 10H); 8.2 (br, 1H); 8.3 (br, 1H); 8.4 (br, 1H); 8.5 (br, 1H); 9.07 (d, J ) 7.4 Hz, 1H, H8). 13C NMR (CDCl3, 100 MHz) δ 19.8 (s); 23.6 (t); 23.7 (t); 24.6 (t); 26.2 (t); 26.6 (q); 26.7 (q); 28.0 (q); 28.3 (q); 28.4 (q); 29.5 (t); 29.7 (t); 30.2 (t); 40.4 (t); 47.1 (t); 54.4 (q); 55.48 (q); 55.53 (t); 55.6 (q); 56.4 (d); 56.5 (d); 56.6 (d); 56.7 (t); 63.1 (d); 63.6 (d); 83.2 (s); 103.5 (d); 104.8 (d); 105.9 (d); 109.8 (s); 111.1 (s); 112.2 (d); 115.4 (d); 116.6 (d); 119.7 (s); 120.3 (d); 122.7 (s); 123.7 (d); 124.4 (s); 127.5 (d); 127.6 (d); 127.7 (s); 128.6 (s); 129.2 (s); 129.8 (d); 129.9 (d); 130.0 (s); 132.9 (s); 133.0 (s); 133.4 (s); 135.0 (d); 135.2 (d); 143.3 (s); 145.0 (s); 146.2 (s); 146.3 (s); 146.9 (s); 150.8 (s); 151.2 (s); 153.4 (s); 155.2 (s); 155.9 (s); 156.0 (s); 156.1 (s); 157.4 (s); 170.4 (s); 171.9 (s); 173.1 (s); 174.7 (s); 175.3 (s). MS (ESI) 884 ([M-Boc+3]/3, 24), 1326 ([MBoc+2]/2, 77). Cell Lines and Culture. Human-derived established cell lines used in this study were purchased from ATCC (American type Culture Collection): A-549, human lung carcinoma (ATCC no. CCL-185); BJ, skin fibroblast (ATCC no. CRL-2522); HT-29, human colorectal adenocarcinoma (ATCC no. HTB-38); and MDA-MB 231, human breast adenocarcinoma (ATCC no. HTB26). All cell lines were maintained in DMEM supplemented


with 10% FBS and 100 units/mL penicillin and streptomycin at 37 °C and 5% CO2. GI50 Analysis. Triplicate cultures were incubated for 72 h in the presence or absence of test compounds Lam-D, 1, 2, 4, and 15 (at ten concentrations, typically ranging from 0.0026 to 10 µg/mL). A colorimetric assay using SRB was adapted for quantitative measurement of cell growth and viability, following a previously described method (23). Cells were plated in 96-well microtiter plates at a density of 5 × 103/well and incubated for 24 h. One plate from each different cell line was fixed, stained, and used for Tz reference (see next paragraph). The cells were then treated with vehicle alone (control) or compounds at the concentrations indicated. Treated cells were incubated for an additional 72 h, and then evaluated for cytotoxicity via colorimetric analysis. The cells were washed twice with PBS, fixed for 15 min in 1% glutaraldehyde solution, rinsed twice in PBS, and stained in 0.4% SRB solution for 30 min at room temperature. The cells were then rinsed several times in 1% acetic acid solution and air-dried. SRB was then extracted in 10 mM trizma base solution and the absorbance measured at 490 nm. Cell survival is expressed as a percentage of control cell growth. Dose-response curves were obtained by using the NCI algorithm (24): Tz ) number of control cells at time t0; C ) number of control cells at time t; and T ) number of treated cells at time t. If Tz < T < C (growth inhibition), then the result is 100 × ([T - Tz]/[C - Tz]). If T < Tz (net cell death), then the result is 100 × ([T Tz]/Tz). After dose-curve generation, the results were expressed as GI50 (the concentration that causes 50% cell growth inhibition, compared to control cultures). General Treatments for Imaging. A-549, MDA-MB-231, and HT-29 cells were seeded onto MatTek (Ashland, USA) glass-bottomed microwell dishes at 30 × 103 cells/cm2. After 24 h, the culture medium was discarded and replaced by fresh DMEM medium containing Lam-D, 1, or 4 at 1 µM. Absence of compound was used as a negative control. Cells were then incubated for 12 h at 37 °C. Topo I-GFP Visualization. Procedure for a single microwell dish transfection: A-549, MDA-MB-231, and HT-29 cells were seeded onto a MatTek (Ashland, USA) glass-bottomed microwell dish at 30 × 103 cells/cm2. Culture medium was discarded after 24 h, cells were washed 3 × PBS, and 1400 µL of reduced serum media Opti-MEM I (Invitrogen, USA) were added. The preparation of DNA for transfection required previous dilution of 3 µL FuGENE (Roche Molecular Biochemicals, Indianapolis, IN) in 100 µL of reduced serum media Opti-MEM I (Invitrogen, USA), and further addition of 6.7 µL of the plasmid solution encoding green fluorescent protein GFP with full-length Topo I (25). The mixture was mixed thoroughly and incubated for 30 min at r.t., before addition to the dish. Samples were incubated at 37 °C and 5% CO2 for 10 h. Afterward, medium was discarded, cells were washed three times with PBS, and new DMEM solution containing 1 µM Lam-D, 1, or 4 was added. Absence of compound was used as a negative control. The cells were incubated for an additional 12 h at 37 °C and then analyzed by confocal microscopy. Confocal Laser Scanning Microscopy. Confocal laser scanning microscopy was performed with a Leica TCS SPII microscope (Leica Microsystems Heidelberg GmbH, Mannheim, Germany), using a 63× objective. GFP fluorescence was excited with an Ar laser excitation at 488 nm. Lam-D and its derivatives were excited at 351 nm. The same microscope settings were


used for each conjugate and concentration. To avoid crosstalk, the two-fluorescence scanning was performed in a sequential mode. Uptake Measurements by Fluorescence-Activated Cell Sorting Flow Cytometry. 1 × 106 A-549, BJ, MDA-MB-231, and HT-29 cells were seeded onto 25 cm2 cell culture flasks (Nalgene Nunc International, Naperville, USA) with 10 mL of DMEM. After 12 h, the culture medium was discarded and replaced by fresh DMEM medium containing compounds 1 µM Lam-D, 1, 2, or 4. Absence of compound was used as a negative control. The cells were then incubated for 12 h at 37 °C. After incubation, the cells were washed three times with PBS, detached with trypsin-EDTA 0.25%, and centrifuged at 1000× rpm. Finally, the medium was decanted, and the cellular pellet was resuspended in PBS and kept at 0 °C until measurements were performed. Fluorescence analysis was performed with a MoFlo cytometer (DakoCytomation, Colorado, USA), using the 351 nm excitation line of an Ar laser (25 mW) and emission detection at 450 nm (tolerance range (65 nm). CIQ is expressed as a percentage value in reference to Lam-D. It was calculated by dividing the fluorescence value of the test compound by the fluorescence value obtained with the Lam-D control under the same experimental conditions.

RESULTS Orthogonal protecting groups had to be used for the three phenol groups of Lam-D and for the functional groups presented into the conjugation building blocks. N-Boc was used to protect the amino and guanidino groups of the oligomeric building blocks 7 and 8. Synthesis of compounds 2-4 required the preparation of different building blocks: the protected Lam-D derivatives 5 and 6, the DTPA-PEG dendrimer 7, and the peptide 8 (Figure 2). Compounds 5 and 6 are the precursors for the conjugates at positions 3 and 4′, respectively, and contain two phenolic groups protected as either TBDPS ethers or Boc esters, respectively. In the protected peptide 8, a glycine was introduced as spacer at the C-terminal position to avoid the steric hindrance caused by the C-terminal Val residue during coupling. Synthesis of Protected Lamellarins 5 and 6. The protecting groups OiPr/OBn used in earlier strategies (9) required harsh deprotection conditions incompatible with the synthesis of more complex Lam-D conjugates such as 4.2 The previously described lamellarin 9 (26, 27), for which three different and orthogonal protecting groups were employed (MOM, Bn, and TBDPS), was used as the precursor to Lam derivatives 5 and 6 (Scheme 1).3 Lam 9 was prepared following Banwell’s strategy for the total synthesis of Lam-K (28). Oxidation of 9 under MW irradiation using DDQ in CHCl3 gave 10 with good yield. Compound 10 was subjected to changes of protecting groups (see Scheme 1). Catalytic hydrogenation of 10 over Pd-C in methanolic EtOAc gave 10a, which was successfully converted into 10b by TBDPS protection of the phenol. Removal of the MOM protecting group at position 3 of 10b with trimethylsilyl iodide in CHCl2 gave 5 in excellent yield. Moreover, compound 10a was subjected to the latter conditions, which afforded the 4′-OTBDPS monoprotected Lam-D 10c in quantitative yield. The free phenol groups of 10c were protected as tert-butyl carbonates using Boc2O, DMAP, and CH2Cl2 to give 10d in quantitative yield. Finally, OTBDPS deprotection of 10d with TBAF in MeOH gave the 4′-OH Lam-D intermediate 6 (85%). As a side note, compounds 10a and 10c are privileged synthetic intermediates for the construction of additional mono2 Conjugate 4 protected with OiPr on positions 3 and 11, and BocLys, Boc-Pro and Pbf-Arg gave only mixtures on deprotection assays. 3 The ester bonds of the protected Lam-D conjugates were labile; hence, to avoid problems with hydrolysis, we minimized the deprotection steps after condensation.


Figure 2. Building blocks for the synthesis. The UV emissions corresponding to Lam-D, 1, and 4 are arbitrarily represented in red tones. The test compounds were seeded at a concentration of 1 µM and then incubated for 12 h.

and diconjugates at positions 11-OH and 3,11-OHs of Lam-D, respectively. Synthesis of Poly(ethylene glycol)-Based Dendrimer 7. PEG-based dendrimer 7 was synthesized by coupling 1-(tertbutyloxycarbonylamino)-4,7,10-trioxa-13-tridecanamine to monobenzyl-protected diethylenetriamine pentaacetic acid with PyBOP and DIPEA. The tetracarboxylic moiety derivative was prepared from an orthogonally protected DTPA derivative (one benzyl and four tert-butyl protecting groups). The tBu groups were eliminated using 4.0 M HCl in dioxane, and then, the benzyl group was eliminated by hydrogenolysis with Pd/C to render dendrimer 7 (29). Synthesis of the Peptide NLS 8. The protected peptide 8 was synthesized on chlorotrityl resin following standard Fmoc/ tBu solid-phase chemistry, with 20% piperidine-DMF for the deprotection steps, and DIPCDI and HOBt as coupling reagents. N-R-Fmoc-N-ω,N-ω′-bis-tert-butoxycarbonyl-L-arginine was used for the synthesis of the NLS peptide sequence. Attempts to use Fmoc-N-ω-Pbf-L-arginine resulted in harsher deprotection conditions and complex reaction crudes. The last amino acid used was Boc-L-Pro-OH (as the desired building block had to be completely protected). The peptide was cleaved from the resin using 3% TFA in CH2Cl2, and after solvent evaporation, it was lyophilized. Esterification and Synthesis of Conjugates 1-4. To test the efficacy of the protecting scheme, the synthesis of bioconjugate 1 was repeated using the following strategy (21). An ester bond between 5 and BocNH-CH2(CH2OCH2)6CH2COOH was formed using EDC · HCl with a catalytic amount of DMAP to

Pla et al.

afford compound 11 (Figure 1) in quantitative yield. Compound 11 was considered a good model for the deprotection assays, because it contains the critical protecting groups and the ester functional group. Hence, it was used for the optimization of procedures and to test the success of the deprotection steps. Initial assays of sequential TBAF-TFA, two-step deprotection led to complex crude products. Furthermore, purification on SiO2 gave low yields of 1. The best results were obtained via simultaneous deprotection of both groups, using liquid HF at low temperature. Highly pure final product was obtained from the reaction crude by precipitation with MTBE. Notwithstanding, the scope of the reaction was limited to small amounts of starting material.4 Compound 1 was synthesized in 84% overall yield from its precursor 5. This is a major improvement over previous OiPr/OBn strategies (45% yield, from 4′,11-diisopropyl-LamD) (9). Formation of an ester bond between 5 and 7 (29) afforded compound 12 (Figure 1) in 26% yield, using EDC · HCl with a catalytic amount of PS solid supported DMAP in CH2Cl2. Deprotection of compound 12 using HF provided 2 in 36% yield. Ester bond formation between 8 and protected lamellarin 5 or 6 using EDC · HCl was unsuccessful. The inaccessibility of the carboxylic acid in the N-Boc protected oligopeptide sequence 8 or steric hindrance of the free phenolic group in Lam-D building blocks 5 and 6 may have been decisive to the lack of reaction. Various attempts at ester bond formation between 8 and the scaffold 5 were also unsuccessful.5 Therefore, taking advantage of the relatively easy amide bond formation (i.e., compared to ester bonds), an N-Boc-Gly-OH spacer was introduced at position 3 of 5 (affording 13 in 89% yield, Figure 2) for subsequent amide bond formation with 8. N-Boc deprotection of 13 with 40% TFA followed by reaction with 8 in EDC · HCl, HOBt, and DIPEA as base gave 14 (Figure 1, 58% yield). Deprotection of 14 with HF under standard conditions afforded the NLS peptidic conjugate 3 in 38% yield. The NLS conjugate at position 4′ of Lam-D could not be formed using the same conditions employed for ester bond formation between 6 and 8.6,7 Instead, preactivation of 8 with TCFH (30) and NEt3 followed by the addition of a solution of 6 and DMAP were required, affording 15 (Figure 1) in 45% yield (relative to 40% transformation of 6). Elimination of the nine Boc protecting groups with 40% TFA in CH2Cl2 gave compound 4 in 17% yield. The ester bond of compound 3, which has a double Gly spacer, is more susceptible to nucleophilic attack by nucleophiles from the medium than that of compound 4, which has a single Gly spacer. Thus, the final conjugate 3 (derived from 14) was water-labile. The rapid degradation of 3 made biological tests with this compound impossible.8 Cytotoxicity and Cellular Uptake. The cytotoxicity of Lam-D and its analogues (1, 2, 4, and 15) was evaluated against BJ human skin fibroblasts, and a panel of three human tumor 4 The yield for the deprotection was 84% working on a 20-30 mg scale. However, the procedure could not be scaled up. The stability 1 was studied in DMEM supplemented with 10% FBS and 100 units/ mL penicillin and streptomycin at 37 °C. HPLC analysis indicates 97% of Lam-D liberation after 360 min of incubation. 5 Esterification of 5 was tested with EDC · HCl, TCFH, or N,N,N′,N′tetramethylcholorformamidyl chloride as activating agent. 6 N-Cbz-Gly-OH was anchored to 6 in quantitative yield. However, further Cbz deprotection could not be performed without concomitant hydrolysis of the conjugate ester bond. 7 Other coupling reagents such as EDC · HCl, DIPCDI, TFFH, PyBOP with HOAt, and MSNT with NMI failed in ester bond formation. 8 Compound 3 quickly hydrolyzes and liberates Lam-D into the medium, even on the time scale of an HPLC analysis.



Scheme 1a

a Reagents and conditions: (i) DDQ, CHCl3, MW, 120 °C, 10 min (81%); (ii) H2, Pd-C, EtOAc, MeOH, r.t., 16 h (95%); (iii) TBDPSCl, Im, DMAP, DMF, r.t., 24 h (58%); (iv) Me3SiI, CH2Cl2 r.t., 20 min (84% for 5; quant. yield for 10c); (v) Boc2O, DMAP, CH2Cl2 r.t., 16 h (quant.); (vi) 1M TBAF in THF, MeOH, -78 °C, 15 min (85%).

Table 1. Cytotoxicity of Compounds 1, 2, 4, and 15 in Three Human Cancer Cell Lines cytotoxicity (M) compound

HT-29 colon

A-549 lung

MDA-MB-231 breast

BJ skin fibroblast

Lam-D 1 2 4 15

3.00 × 10-6 1.68 × 10-6 3.92 × 10-6 1.01 × 10-6 1.94 × 10-6

1.22 × 10-7 8.86 × 10-8 2.20 × 10-7 4.79 × 10-8 n.d.

1.34 × 10-7 4.07 × 10-8 8.31 × 10-8 4.79 × 10-8 1.24 × 10-6

6.37 × 10-9 6.51 × 10-9 1.54 × 10-8 3.14 × 10-8 -

cell lines: A-549, HT-29, and MDA-MB-231 (Table 1). A conventional colorimetric assay was used to estimate values of GI50 (defined here as the drug concentration that causes 50% of cell growth inhibition after 72 h of continuous exposure to the test molecule). Lam-D was included for comparison. The results are shown in Table 1. The tested compounds in the tumor

cell lines exhibited cytotoxicities from 4 µM to 40.7 nM, except for the Boc protected derivative 15, which only had micromolar activity for the HT-29 and MDA-MB-231 cell cultures. BJ skin fibroblasts were used in the present study to evaluate the effects of the drug and its conjugates in normal cells. In this nontumoral cellular culture, conjugate 1 citotoxicity was similar to that of Lam-D, or even 2.4-4.9-fold less for 2 and 4. FACS flow cytometry was used to measure cellular uptake quantification (9). The results are shown in Table 2. Interestingly, the cellular internalization quotient for the PEGylated derivatives 1 and 2 were higher than that of Lam-D in all cancer cell lines. Indeed, compound 4, with an NLS sequence, was 10 times more active than Lam-D in A-549 and MDA-MB-231 cell lines and retained CIQ, despite having the highly charged NLS peptide. CIQ of conjugates in BJ cellular culture were from 76.8% to 128.6%.

Table 2. Cellular Internalization as Measured by FACS cellular internalization quotient (CIQ)a

cellular internalization (AU)

compound HT-29 colon A-549 lung MDA-MB-231 breast BJ skin fibroblast HT-29 colon A-549 lung MDA-MB-231 breast BJ skin fibroblast Lam-D 1 2 4 a

82.7 88.0 83.7 88.5

328.5 393.0 374.9 377.7

443.8 527.5 455.3 434.9

CIQ was calculated in reference to the cellular uptake of Lam-D.

259.4 333.4 199.2 240.6

100%a 106% 101% 107%

100%a 120% 114% 115%

100%a 119% 103% 98%

100%a 128.6% 76.8% 92.8%


Pla et al.

Figure 3. Internalization of Lam-D and conjugates 1 and 4 by Topo I-GFP transfected cells.

Cellular Distribution of Lam-D, 1 and 4. Tracking in GFP-Topo I Transfected Cell Cultures. Lam-D is a Topo I inhibitor. To determine whether Lam-D, 1, and 4 localize to the same subcellular compartment as Topo I, a cellular localization assay was performed. A functional chimera of the green fluorescent protein EGFP with full-length Topo I (GFP-Topo I) was expressed in HT-29, A-549, and MDA-MD-231 cells, which were then treated with either Lam-D, 1, or 4. As described, GFP-Topo I was located in the nucleus (25) in all cell types (Figure 3, positive control). Conjugate 4, carrying the NLS signal, was localized to the nucleus in HT-29 and A-549 cells (Figure 3, j1, j2, k1, and k2), suggesting that its higher activity could correlate to subcellular colocalization with its target, Topo I. Interestingly, Lam-D and 1 showed both higher activity and greater nuclear localization in MDA-MB-231 cells than 4 did (Figure 3, f1, f2, i1, and i2).

DISCUSSION We have described the synthesis of Lam-D conjugates with well-defined, water-soluble peptidic and dendritic systems as potential nontoxic drug delivery vehicles. Interestingly, the Lam-D conjugate containing a single backbone attached to a phenolic residue of Lam-D has very different solubility compared to Lam-D alone. Scaffold 10, with three orthogonal protecting groups, has proven to be a good starting material, enabling synthesis of 5 and 6, via protection group interchange, on a multigram scale and in good overall yield. New protected derivatives of Lam-D, which can be conjugated to one (C11-OH, 10a) or two (C3-OH and C11-OH, 10b) phenol groups, have been isolated in good yields with this strategy. Compound 1 was synthesized in 84% overall yield from its precursor 5; this constitutes an important improvement over previous strategies (45% yield, from 4′,11-diisopropyl-Lam-D) (9). Simultaneous removal of TBDPSO and NBoc with HF is a new and highly efficient deprotection scheme for compounds with labile ester bonds. The OBoc and TBDPSO protecting groups used in lamellarins 5 and 6 permitted optimization of the final deprotection conditions and represented adequate choices for total deprotection in the last step. Thus, single-step HF deprotection

was the cleanest method for preparing Lam-D 1-3 (9-84% overall yields from 5). The new Lam-D conjugates reported here are excellent candidates for further biological evaluation. The evaluation of conjugates 3 and 4 in BJ skin fibroblasts as normal cells was used in the present study. In this cellular culture, no significant variation or even less cytotoxicity was obtained for conjugates 3 and 4 than the parent compound Lam-D. PEGylated conjugates 1 and 2 have much higher cytotoxicity to MDA-MB-231 cells than Lam-D alone. Surprisingly, compound 4 had nanomolar GI50 for MDA-MB-231 and A-549, representing 10-fold-lower GI50, respectively, compared to Lam-D. These results in the A-549 cancer cell line could correlate to colocalization of 4 in nuclear regions where GFP-Topo I accumulated (Figure 3k). The NLS peptidic sequence is at least partly responsible for nuclear import of 4 in A-549 and HT-29 cell lines. In contrast, Lam-D and 1 were able to weakly reach the nucleus in only MDA-MB-231 cells. Altogether, we conclude that better cytotoxicity correlates with greater nuclear localization. In summary, the use of a robust chemistry strategy, with a combination of solid-phase and solution strategies and a myriad of orthogonal and/or compatible protecting groups, has allowed the preparation of several Lam-D bioconjugates. All of them show some improved characteristics when compared with the parent lamellarin D. Particularly, 4, which contains the NLSpeptide, shows a clearly improved cytotoxicity and a colocalization in the nucleus. To the best of our knowledge, 4 is one of the first examples of NLS peptide conjugation with small molecules. Our results (9) indicate that Lam-D derivatives obtained through various chemical modifications may have markedly higher activity than the parent compound in certain tumor cell lines, increasing the selectivity between the tumor cell lines.

ACKNOWLEDGMENT This study was partially supported by CICYT (Grant BQU 2006-03794 and BQU2005-00315), Generalitat de Catalunya, and the Barcelona Science Park. We gratefully acknowledge PharmaMar S.A. for performing the preliminary biological tests, and the Networking Centre on Bioengineering, Biomaterials and


Nanomedicine (CIBER-BBN). This study was partially supported by the Industrial Consortium “NanoFarma” from the Spanish grants of CENIT program. We thank Dr. J. Comas from Flow Cytometry Facility - SCT (UB) for valuable discussions regarding the present work. We also thank Prof. C. Mielke (Heinrich-Heine University, Medical School, Du¨sseldorf) for generous donation of a sample of GFP-Topo I plasmid.

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Lamellarin D Bioconjugates II: Synthesis and Cellular Internalization of

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